Palygorskite has shown satisfactory performance in salted water-based fluids, especially as a rheological agent. However, this type of formulation has been used in the petroleum industry only in well drilling operations. This study proposes the development of a salted water-based fluid with palygorskite, which presents an adequate performance as a liquid barrier element in temporary abandonment operations of wells. Based on a factorial design, seven fluid formulations were prepared with varying concentrations of palygorskite and PAC LV and were tested by measuring the HPHT filtrate volume, rheological properties, density, and pH. For comparison purposes, the results of the seven formulations were evaluated against a formulation without palygorskite and analyzed for their performance in abandonment operations. The results showed that the presence of palygorskite reduces filtrate volumes by at least 21%, thereby helping control the pressure exerted by the fluid column, which is the primary requirement for abandonment operations. Furthermore, the fluid that contained the highest amount of palygorskite and PAC LV (20 g and 8 g, respectively) showed the best results regarding filtrate control (11.2 mL) and solid sedimentation. Therefore, it is a very promising alternative for use as a well barrier element in the temporary abandonment of wells.

This study aims to evaluate how the operational procedure adopted for pellet placement and the exposure to subsurface conditions influence the mechanical integrity of bentonite plugs used as barrier elements in the abandonment of petroleum wells. To this end, the plugs were formed by hydrating the pellets directly in water, simulating the onshore procedure, while the offshore plugs were obtained from pellets hydrated in deionized water after immersion in diesel or olefin, which are suggested as displacement fluids. The plugs obtained were tested by compression and adhesion tests. These mechanical tests were also carried out for specimens obtained from plugs exposed to four formulations of synthetic formation waters. The results obtained demonstrated that, in the offshore procedure, the previous contact with olefin may adversely affects the mechanical stability of bentonite plugs, while plugs formed from pellets immersed in diesel presented satisfactory mechanical properties. However, the contact with formation water evidenced that the onshore plug presents superior resistance than the offshore plug previously immersed in diesel. The highly successful performance of the onshore plug was attested by the maintenance of the compressive strength, which exhibited a maximum reduction of 13%, even after exposure to the most saline formation waters.

One of the operational challenges regarding the use of bentonite pellets as sealing materials in the abandonment of offshore fields consists of their placement inside the well. This study aimed to analyze the interaction of fluid media, consisting of saline solutions (NaCl, CaCl₂ and KCl) and organic compounds (diesel, glycerin and olefin), with bentonite pellets, for their applications as displacement fluids in offshore oil well abandonment operations. The physical integrity of the bentonite pellets in contact with the fluids was verified through visual inspections and dispersibility tests. Linear swelling tests were also performed to evaluate the swelling potentials of the pellets in deionized water after their contact with the fluid media. The results indicated that the NaCl, CaCl₂ and KCl solutions completely compromised the physical integrity of the pellets, while diesel and olefin showed the best responses regarding the structural preservation. Furthermore, the linear swelling tests showed that, even after the contact with diesel and olefin for 1 h, the bentonite pellets reached a total swelling of 78% in water after 24 h. In this way, diesel and olefin proved to be highly promising alternatives to be used as displacement fluids for bentonite pellets in wells that will be abandoned in a submarine environment.

As reações para a síntese de biodiesel podem ser homogêneas ou heterogêneas, a depender do catalisador utilizado, sendo a heterogênea a melhor alternativa por permitir que o catalisador seja recuperado após a reação. Este trabalho teve como objetivo analisar a eficiência do catalisador magnético do tipo ferrita (Ni0,5Zn0,5Fe2O4), em reação de transesterificação, antes e após a sua recuperação. A taxa de conversão em biodiesel foi determinada por cromatografia gasosa. Os resultados mostraram que, no terceiro reuso, a taxa de conversão caiu de 80,25% (amostra de catalisador virgem) para 68,31%. Isto indica que a recuperação e posterior reuso é viável, pois as características catalíticas ainda podem ser mantidas.

This study aims to evaluate how the operational procedure adopted for the pellets placement and the exposure to subsurface conditions influences the mechanical integrity of bentonite plugs used as barrier elements in the abandonment of petroleum wells. To this end, two methodologies were used to obtain the plugs: from the first methodology, the pellets were immersed in diesel or olefin, which are proposed as displacement fluids in offshore operations, and then, hydrated in deionized water; in the second methodology, representative of onshore operations, the pellets were directly hydrated in deionized water. After that, the plugs were tested by compression and adhesion tests. These mechanical tests were also carried out for test specimens obtained from plugs exposed to four formulations of synthetic formation waters. The results obtained demonstrated that the previous contact with olefin adversely affects the mechanical stability of bentonite plugs, while plugs formed from pellets immersed in diesel presented satisfactory mechanical properties. The mechanical properties of onshore plugs attested the highly successful performance of these elements, once its compressive strength was minimally impacted by exposure to formation waters and more pronounced reductions were observed only in the adhesion properties after the contact with higher salinity formation waters.

Polymeric fluids are widely applied in workover operations because of their ability to control well pressure, regulate filtrate loss, and preserve reservoir productivity. However, their performance is highly dependent on polymer stability, since degradation under thermal, mechanical, or chemical stresses can compromise rheology, weaken filtration control, and increase the risk of formation damage. Research since the 1970s has advanced toward developing improved formulations, aiming to enhance efficiency while reducing reservoir impairment. Laboratory characterization techniques have been essential in evaluating polymer degradation and fluid–rock interactions, generating insights for polymer selection and fluid design. Within this context, this study proposes a literature review on polymeric fluids in workover operations, with emphasis on the role of polymers in fluid formulation and performance. The review also addresses operational fundamentals and technical challenges, focusing on thermal stability, degradation mechanisms, and strategies to minimize formation damage through adequate formulation and characterization approaches.